If it is desired to produce a portion of a mixture of two flowable components which must be in a particular quantitative ratio to one another, two piston-and-cylinder syringes can be used which are coupled to one another for the joint movement of their pistons. The quantitative ratio of the components is then determined by the cross-sectional ratio of the pistons. An important field of application of such coupled syringes is in dental technology, specifically the initial mixing of multicomponent resins as fillers or of an impression compound. Known systems for the release of equal proportions of flowable substances comprise an appliance in which the pistons of the two syringes are synchronously advanced (EP-B-0 492 413, EP-A-1 010 401, WO 91/05 731). In these, not only are the syringe bodies rigidly held side by side but, by means of push rods connected to one another, the pistons are likewise rigidly connected to one another, each adopting the same position in the associated syringe bodies. It follows also that the states of emptying of the two syringe bodies must always coincide. This causes no problem if one component is always used with the same other component and the syringes containing them are therefore only used together. However, there are cases in which this condition is not satisfied. For example, there are dental resins which as a rule are used without a second component and are then cured by means of radiation, but which exceptionally are also used in mixtures containing a curing agent as the second component. In these cases, it has hitherto been necessary to meter the components individually. and mix them by hand. Systems are also known in which two syringes, which contain components assigned to one another, are prepared separately and brought together in specific cases for application in a single appliance (WO 91/05 371, U.S. Pat. No. 4,260,077, U.S. Pat. No. 5 104 375). A necessary condition here is that the levels of filling coincide.
It would be expedient, where the basic component remains the same and is to be used variably in specific cases with or without an additional component, always to be able to use the same syringe, while the syringes for the additional components can be combined therewith as desired and without regard to their random level of filling. It is an object of the invention to provide a system which permits this.
According to the claims, provision is made for both the syringe bodies and the syringe pistons to be able to be rigidly coupled to one another in the direction of advance by releasable coupling devices irrespective of the current piston position. The coupling devices are so formed that the pistons and/or the syringe bodies can be connected to one another (in the direction of advance) in any desired relative position. A system is preferred in which the syringe bodies can be coupled to one another only in a predetermined relative position but the piston rods belonging to the pistons can be coupled to one another in any desired relative position.
The devices for coupling the syringe bodies to one another may be provided separately from the latter. It is more expedient, however, to provide the syringe bodies themselves with mutually fitting coupling devices. They are expediently fixedly connected to at least one thereof or form a fixed component thereof.
The syringe bodies are generally provided at their front ends with a release pipe. If two components are released together, they are in general processed together, and may or may not also be released jointly from a mixing device. It is therefore expedient to form the coupling device for the syringe bodies in such a way that their release pipes are located close together or at least in a defined position relative to one another. In order to ensure this in the direction of advance, provision may be made, according to the invention, for a part of the coupling device provided on one of the two syringe bodies or to be attached to be formed as a stop for a frontal surface of the other syringe body, counter to the direction of advance. In order to ensure this transversely to the direction of advance, the device for coupling the syringe bodies may be so formed that the release pipe of at least one of the two syringe bodies may thereby be localized transversely to the direction of advance. The transverse distance between the release pipes is especially important if a nozzle for the joint release, with or without mixing, of the two substances. According to the invention, the coupling device can be provided with a device for the releasable retention of such a nozzle. For the relative securing of the syringe bodies in the direction of advance, the single stop mentioned may be sufficient. More expediently, however, a second stop is provided additionally or instead and additionally secures the syringe body, which is secured in one direction by the front stop, in the other direction also. This is expediently achieved by a more rearward part of the coupling device.
In order for the syringe bodies to remain in the coupled position, suitable fixing means are expediently provided, these being formed, for example, by a snap-fit mounting.
The syringe bodies are expediently coupled to one another in parallel, so that the mutually coupled sections of the piston rods remain at a constant distance from one another during their advance.
The device for coupling the piston rods may be fixedly disposed at the end of one of the two piston rods. This means that the other piston rod has to be approximately twice as long to ensure that an effective coupling connection can be formed even if the syringe provided with the coupling device for the piston rods is still full but the other is nearly empty. This does not apply if a separate coupling is used or if both piston rods bear a coupling device.
The coupling device for the piston rods is expediently formed as a clamp, in order, under the action of the force of a spring closing it, to enclose the piston rod in question so firmly that a sufficient friction is generated for entrainment in the direction of advance. However, closure devices may also be provided thereon which generate this coupling force.
In order to permit a firm grip of the clamp on the piston rod, the surfaces of the two are expediently formed to engage into one another. For this, even a roughening is sufficient, the peaks of the roughnesses thereof engaging randomly into the troughs of the roughnesses of the respective other surface. The surfaces may however also be regularly gridded or ribbed (transversely to the direction of advance). Such structures should be so fine that they do not lead to a substantial change in the existing statuses of the pistons when the clamps are applied.